| The field of photocatalysis can be traced back more than 80 years to early observations of the chalking of titania-based paints and to studies of the darkening of metal oxides in contact with organic compounds in sunlight. During the past 30 years, due to its practical application in air (or water) remediation and self-cleaning surfaces, photocatalytic technology has become an extremely hot research point.Currently, the titania is the most studied photocatalyst owing to its high photocatalytic activity, good chemical stability, low cost and non-toxic, no secondary pollution, and decomposition of certain organic compounds to carbon dioxide and water completely. However, its drawbacks, such as the low quantum efficiency, low efficiency under solar light radation, and difficult to recovery, make it difficult to be widely used. How to increased the photocatalytic activity of TiO2 under visible light and be able to reuse become the research focus. The fixation of the TiO2 photocatalyst onto a substrate can effectively promote the separation of electrons and holes, thus improve the quantum efficiency. In addition, coating of TiO2 on the supporter which has greater surface area and high mechanical strength, can effectively promote its reusability. In this paper, we used carbon nanomaterials modified porous alumina as a carrier to prepare the supported TiO2 photocatalyst. The effects of the carbon nanomaterials-alumina composite on the photocatalytic properties of titanium dioxide were detailedly studied.In the experiment, aluminum nitrate as the precursor was used to prepared alumina-carbon nanotube composite through precipitation method. MWCNT-Al2O3 was then used as carrier to prepare TiO2/MWCNT-Al2O3 photocatalyst by a simple impregnation method. N doped TiO2 were prepared by the sol-gel method, therein, tetrabutyl titanate was the precursor and N was from urea. The photocatalysts were characterized through the methods such as XRD, DRS and SEM. The results on various photocatalysts prepared by different methods have been discussed in details. We obtained the optimised experimental parameters and ideal preparation method based on the result of photocatalytic activities of methylene orange degradation or sulfur recovery in liquid phase.(1) The preparation and studies of TiO2/Al2O3-MWCNTIn this part, Multiwalled carbon nanotube (MWCNT) doped-Al2O3 (MWCNT-Al2O3) was prepared by sol-gel method. MWCNT-Al2O3 was used to prepare TiO2/MWCNT-Al2O3. The morphology and structure of photocatalyst has been characterized through the methods such as XRD, TEM, SEM, BET, EDS. The optical properties of photocatalyst have been characterized through UV-Vis DRS, PL. XRD results showed that the samples of TiO2 were anatase. TEM and SEM showed that TiO2 highly dispersed on surface of Al2O3-MWCNT. The results of N2 adsorption-desorption expriment show that the average pore diameter of TiO2/AlO3-MWCNT was 5.97nm, the specific surface area wase 309.75 m2·g-1. UV-Vis DRS and PL results indicated that agglomeration of the TiO2 was reduced and the absorption capacity was enhanced due to the presence of MWCNT. In addition, the results of photocatalytic degradation of MO solution indicated that the photocatalytic activity of TiO2/Al2O3-MWCNT was significantly higher than that of the pure TiO2 and TiO2/Al2O3. The photocatalytic activity still remained 60% after four runs, which noticeably higher than pure TiO2. (2) The preparation and studies of TiO2/Al2O3-grapheneIn this part, we synthesized graphene materials by the oxidation-reduction method. The prepared process of TiO2/Al2O3-graphene composite was same as the above-mentioned. XRD, SEM and UV-Vis results showed that all samples are anatase, and there have a blue shift in absorbing wavelengths. Moreover, the photocatalytic activity of TiO2/Al2O3-graphene were improved greatly by introducing graphene. Here, we also studied the effect of series of experimental parameters on the photocatalytic properties affirmed by degradation rate of MO. When the amount of doped graphene was 5%, the loadings of TiO2 was 30%, we got the highest photocatalytic activity.(3) The preparation and studies of N doped TiO2/Al2O3-MWCNTIn this part, we prepared N doped TiO2/Al2O3-MWCNT composites through the traditional sol-gel method. XRD characterization indicated that the TiO2 in the samples are anatase. The nitrogen mitht enter into the TiO2 lattice, therefore, it can not be observed any characteristic diffraction peaks of the nitrogen compounds in XRD patterns. The activity of nitrogen-doped samples was evaluated base on photocatalytic sulfur recovery under visible light, and obtained the optimum conditions for preparating catalysts. The rate of photocatalytic sulfur recovery for the N-doped samples was much higher than the non-doped ones. The reason may be attributed to the replacement of oxygen vacancies in the TiO2 lattice by nitrogen leading to band gap reduce, and increased sun-light availability. The threshold existed in ratio of N/Ti. The optimal content of N was 5%, and the best sulfur recovery rate of 60% was obtained. |
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